Adaptive vertical take-off and landing propulsion system

ABSTRACT

A propulsion system for an aircraft includes a plenum having an intake port and an output port. A fan is coupled to a motor configured to power the fan, and the powered fan is configured to compress ambient air entering the intake port. One or more ejectors are fluidically coupled to the plenum via one or more valves. A nozzle is disposed within the output port and includes a set of vanes. The system operates in a first configuration in which the nozzle vanes are closed and the compressed ambient air exits the plenum only through the one or more valves into the one or more ejectors. The system operates in a second configuration in which the one or more valves are closed, the nozzle vanes are open and the compressed ambient air exits the plenum only through the output port.

PRIORITY CLAIM

This application claims priority to U.S. Provisional Application No.62/758,441, filed Nov. 9, 2018, U.S. Provisional Application No.62/817,448, filed Mar. 12, 2019 and U.S. Provisional Application No.62/839,541, filed Apr. 26, 2019, the entire disclosures of which arehereby incorporated by reference as if fully set forth herein.

This Application is a continuation-in-part of Application No.PCT/US2019/032988 filed May 17, 2019, which claims the benefit of U.S.Provisional Application No. 62/673,094 filed May 17, 2018.

This Application is a continuation-in-part of Application No.PCT/US2019/034409 filed May 29, 2019, which claims the benefit of U.S.Provisional Application No. 62/677,419 filed May 29, 2018.

This Application is a continuation-in-part of application Ser. No.16/020,116 filed Jun. 27, 2018, and application Ser. No. 16/020,802filed Jun. 27, 2018, both of which claim the benefit of U.S. ProvisionalApplication No. 62/525,592 filed Jun. 27, 2017.

This Application is a continuation-in-part of application Ser. No.15/685,975 filed Aug. 24, 2017, and application Ser. No. 15/686,052filed Aug. 24, 2017, both of which claim the benefit of U.S. ProvisionalApplication No. 62/380,108 filed Aug. 26, 2016 and 62/379,711 filed Aug.25, 2016.

This Application is a continuation-in-part of application Ser. No.15/670,943 filed Aug. 7, 2017, which claims the benefit of U.S.Provisional Application No. 62/371,612 filed Aug. 5, 2016; 62/371,926filed Aug. 8, 2016; 62/379,711 filed Aug. 25, 2016; 62/380,108 filedAug. 26, 2016; 62/525,592 filed Jun. 27, 2017; and 62/531,817 filed Jul.12, 2017.

This Application is a continuation-in-part of application Ser. No.15/654,621 filed Jul. 19, 2017, which claims the benefit of U.S.Provisional Application No. 62/371,612 filed Aug. 5, 2016; 62/371,926filed Aug. 8, 2016; 62/379,711 filed Aug. 25, 2016; 62/380,108 filedAug. 26, 2016; 62/525,592 filed Jun. 27, 2017; and 62/531,817 filed Jul.12, 2017.

This Application is a continuation-in-part of application Ser. No.15/368,428 filed Dec. 2, 2016; which claims the benefit of ApplicationNo. 62/263,407 filed Dec. 4, 2015.

This Application is a continuation-in-part of Application No.PCT/US2016/064827 filed Dec. 2, 2016; which claims the benefit ofApplication No. 62/263,407 filed Dec. 4, 2015.

This Application is a continuation-in-part of application Ser. No.15/456,450 filed Mar. 10, 2017; which claims the benefit of ApplicationNo. 62/307,318 filed Mar. 11, 2016; and is a continuation-in-part ofapplication Ser. No. 15/256,178 filed Sep. 2, 2016; which claims thebenefit of Application No. 62/213,465 filed Sep. 2, 2015.

This Application is a continuation-in-part of Application No.PCT/US2017/021975 filed Mar. 10, 2017; which claims the benefit of62/307,318 filed Mar. 11, 2016.

This Application is a continuation-in-part of application Ser. No.15/221,389 filed Jul. 27, 2016; which claims the benefit of ApplicationNo. 62/213,465 filed Sep. 2, 2015.

This Application is a continuation-in-part of Application No.PCT/US2016/044327 filed Jul. 27, 2016; which claims the benefit ofApplication No. 62/213,465 filed Sep. 2, 2015.

This Application is a continuation-in-part of application Ser. No.15/625,907 filed Jun. 16, 2017; which is a continuation-in-part ofapplication Ser. No. 15/221,389 filed Jul. 27, 2016; which claims thebenefit of 62/213,465 filed Sep. 2, 2015.

This Application is a continuation-in-part of application Ser. No.15/221,439 filed Jul. 27, 2016; which claims the benefit of ApplicationNo. 62/213,465 filed Sep. 2, 2015.

This Application is a continuation-in-part of Application No.PCT/US16/44326 filed Jul. 27, 2016; which claims the benefit ofApplication No. 62/213,465 filed Sep. 2, 2015.

This Application is a continuation-in-part of application Ser. No.15/256,178 filed Sep. 2, 2016; which claims the benefit of ApplicationNo. 62/213,465 filed Sep. 2, 2015.

This Application is a continuation-in-part of Application No.PCT/US2016/050236 filed Sep. 2, 2016; which claims the benefit ofApplication No. 62/213,465 filed Sep. 2, 2015.

All of the aforementioned applications are hereby incorporated byreference as if fully set forth herein.

COPYRIGHT NOTICE

This disclosure is protected under United States and InternationalCopyright Laws. © 2019 Jetoptera. All rights reserved. A portion of thedisclosure of this patent document contains material which is subject tocopyright protection. The copyright owner has no objection to thefacsimile reproduction by anyone of the patent document or the patentdisclosure, as it appears in the Patent and Trademark Office patent fileor records, but otherwise reserves all copyrights whatsoever.

BACKGROUND

One of the main challenges of designing a Vertical Take-off and Landing(VTOL) aircraft is sizing the propulsion system to be efficient in bothVTOL and hover phases as well as cruise conditions. Since the propulsionsystem fraction of the total weight needs to be kept low to maximizepayload and fuel reserves, the challenge is how to employ a system thatproduces roughly 4-6 times more thrust at take-off (inlift-by-thrust-only mode) or in hover, compared to in wing-borne andcruise conditions. In the first case the thrust is balancing the weightof the aircraft and much larger engines and power or thrust arerequired, whereas in cruise conditions the size of the engine needs tobe much smaller to balance drag as the wings of the aircraft balance theweight.

Traditionally VTOL was achieved with either separate systems(lift/cruise compromising weight but separating propulsion) or purerotorcraft such as helicopters (compromising wing-borne capabilities).The most successful aircraft employing VTOL capabilities use the samesystem for both vertical and wing-borne phases. Examples are jump-jetssuch as Harrier Hawker, which vectors its turbofan jets (but ends upoversizing the engine for the missions in wing-borne phase) and the V22Osprey, which utilizes turboprops with tilting capabilities. Thetilt-rotor approach is not without risks including vibrations, vortexring state (VRS) and large footprints, as well as complex architectures.

For smaller systems (i.e., 2-4 passenger aircraft) especially in thegrowing Urban Air Mobility market, large lift+cruise airplanes are thedominant design. Especially for electric VTOL, this results in verylarge footprint and moving parts between 8-16 large rotors forefficiency reasons. The wingspan for carrying 4-6 passengers may be aslarge as the wingspan of a small regional plane. The weight of theaircraft due to today's low energy density batteries also imposelarge-size wings and complex operation with the multi-rotors, increasingrisk.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

Preferred and alternative embodiments of the present invention aredescribed in detail below with reference to the following drawings:

FIG. 1 shows a perspective view of an embodiment in trimetric view inVTOL configuration;

FIG. 2 shows a perspective trimetric view of a cruise configuration withFPS system elements used as air brakes for transition to VTOL accordingto an embodiment;

FIG. 3 shows a perspective view of variable vanes in VTOL configurationaccording to an embodiment;

FIG. 4 shows a perspective view of variable vanes in full cruiseconfiguration with FPS system elements extended for airbraking accordingto an embodiment;

FIG. 5 shows a perspective view of the mid-transition from VTOL towingborne configuration and 45-degree FPS system elements while theaircraft accelerates only due to FPS system elements according to anembodiment;

FIG. 6 shows a perspective view of the system elements in cruiseconfiguration according to an embodiment;

FIGS. 7-8 show an alternative embodiment of the invention, usingwing-integrated FPS system elements that allows the thrust augmentingdevices to be hidden during forward flight; and

FIG. 9 is a cross-section of an ejector of an embodiment of the presentinvention depicting the upper half of the ejector and profiles ofvelocity and temperature within the internal flow.

DETAILED DESCRIPTION

This patent application is intended to describe one or more embodimentsof the present invention. It is to be understood that the use ofabsolute terms, such as “must,” “will,” and the like, as well asspecific quantities, is to be construed as being applicable to one ormore of such embodiments, but not necessarily to all such embodiments.As such, embodiments of the invention may omit, or include amodification of, one or more features or functionalities described inthe context of such absolute terms.

A fluidic propulsion system (FPS) according to an embodiment introducesan alternate approach where thrusters without rotating parts can betilted for transitioning from hovering to cruise. During VTOL and hover,thrust augmentation can be obtained using a pressurized fluid as source.One or more embodiments may include a system that is used in all phasesof flight (vertical and wing-borne) while still obtaining anaugmentation for thrust in a forward moving direction.

An embodiment includes a lift+cruise solution involving a source ofcompression such as a fan or compressor of fluids including air, as wellas a dual capability to switch from an augmented thrust in verticalflight (VTOL+hover) and a separate turbofan configuration in cruise.Such a configuration and operation would eliminate the restriction inspeed and allow a VTOL vehicle to move forward at very high velocity,higher altitude capabilities and operate very efficient by loweringsignificantly the fuel burn (specific fuel consumption.)

More descriptively, a fan or compressor or similar machine receivesmechanical work and compresses ambient air to a pressure ratio ofbetween 1.5-2.5. The component may have one or several stages and may bedriven preferably by a gas turbine stage such as the free turbine of aturboshaft engine, without the need of a reduction gear. This element isoptionally advantageous as the weight and moving parts reduction willallow a lighter and simpler construction to be employed.

Referring to FIG. 1, a shaft 11 receives the mechanical power from thefree turbine of a turboshaft or electric motor, and transmits the powerto a fan 21 to compress the air to the aforementioned pressure ratios.The air is pumped into a plenum 12 immediately downstream of the fan 21,and from there the air may be directed into side ports 13 and 14 oraxially downstream through a nozzle having variable vanes 16. Vanes 16can be fully closed or fully opened via mechanisms known in the art. Forexample, one such mechanism could be the variable guide vanes employedin a typical compressor. Another mechanism could be a mechanical screwrotating the hub of the vanes 16 and forcing the vanes to close. Whenclosed as seen in FIGS. 1 and 3, the entire flow from the fan 21 isforced into the side ports 13 and 14 of the plenum 12 and into FPSsystem elements 17, 18 connected fluidically to the plenum 12 via valves15.

In one embodiment the fan 21 receives a power of, for example, 1000 kWfrom a free turbine of a gas turbine of the turboshaft type that spinsat, for example, 25,000 RPM. This value is typical of a machine such asa typical turboprop architecture, before the reduction gear, at fullspeed. Such power and speed can yield a compressed air stream of, e.g.,1.8 atmospheres (a pressure ratio of 1.8 or 180 kPa approximately) and aflow of circa 15 kg/s assuming an efficiency of 80% on the part of thefan.

The fan 21 itself may be manufactured of ultralight materials such astitanium or even composite materials, the former using wide chord,compound swept fan blades for higher efficiency and manufactured in onepiece as a blisk. A design with low noise features is included.

At 15 kg/sec, 180-200 kPa total pressure, and assuming an airtemperature of 353 Kelvin, stream 22 is split and transmitted to FPSelements 17, 18 embedded within an airframe of an aircraft. The FPSelements 17, 18, which are described in greater detail as ejectors in,for example, U.S. patent application Ser. No. 15/221,389 filed Jul. 27,2016 and Ser. No. 15/256,178 filed Sep. 2, 2016, which are herebyincorporated by reference as if fully set forth herein, can augment thethrust which would otherwise result from accelerating and expanding theflow simply to the atmospheric pressure to at least 2:1 and up to 3:1ratios. In this example, the thrust achieved via ejector augmentation isgiven in Equation 1 below:

$\begin{matrix}{{2*15\mspace{14mu} {{kg}/s}*\sqrt{1.4*287\frac{J}{kgK}*353\mspace{14mu} K}} = {11.3\mspace{14mu} {kN}\mspace{14mu} {thrust}}} & {{Eq}.\mspace{14mu} 1}\end{matrix}$

as opposed to a thrust of 5.65 kN if a simple nozzle is employed. Inthis case 287 J/kg-K is the air constant, 1.4 is the air exponentialfactor, 353 K is the discharge temperature from the fan 21 compression,2 is the augmentation ratio and 15 kg/s is the total mass flow rate.

With further optimization of the FPS elements 17, 18, the total thrustmay reach an augmentation ratio of 2.5, meaning 14.122 kN, for the sameamount of mechanical input power of 1000 kW supplied to the fan 21.

FIG. 9 illustrates a cross-section of the upper half of an ejector 200,the structure and functionality of which is similar or identical to thatof elements 17, 18. A plenum 211 is supplied with hotter-than-ambientair (i.e., a pressurized motive gas stream) from, for example, acombustion-based engine that may be employed by the vehicle. Thispressurized motive gas stream, denoted by arrow 600, is introduced viaat least one conduit, such as primary nozzles 203, to the interior ofthe ejector 200. More specifically, the primary nozzles 203 areconfigured to accelerate the motive fluid stream 600 to a variablepredetermined desired velocity directly over a convex Coanda surface 204as a wall jet. Additionally, primary nozzles 203 provide adjustablevolumes of fluid stream 600. This wall jet, in turn, serves to entrainthrough an intake structure 206 secondary fluid, such as ambient airdenoted by arrow 1, that may be at rest or approaching the ejector 200at non-zero speed from the direction indicated by arrow 1. In variousembodiments, the nozzles 203 may be arranged in an array and in a curvedorientation, a spiraled orientation, and/or a zigzagged orientation.

The mix of the stream 600 and the air 1 may be moving purely axially ata throat section 225 of the ejector 200. Through diffusion in adiffusing structure, such as diffuser 210, the mixing and smoothing outprocess continues so the profiles of temperature (800) and velocity(700) in the axial direction of ejector 200 no longer have the high andlow values present at the throat section 225, but become more uniform atthe terminal end 100 of diffuser 210. As the mixture of the stream 600and the air 1 approaches the exit plane of terminal end 100, thetemperature and velocity profiles are almost uniform. In particular, thetemperature of the mixture is low enough to be directed towards anairfoil such as a wing or control surface.

When vanes 16 are closed and the fan 21 supplies this power, enoughthrust may be obtained from such a system to enable lifting of anaircraft that weighs, for example, between 1100 and 1400 kgs. This typeof aircraft may direct the thrust upwards via swiveling FPS elements 17,18 supplied from the fan 21 via ports 13 and 14, which can also rotatewith respect to their principal axes via swiveling joints 23. Theswiveling or vectoring of FPS elements 17, 18 can change the attitude ofthe aircraft first in vertical takeoff, further in hovering via smallangle changes and finally in transition to wing borne operation viaswiveling of the FPS elements to direct the thrust at 45 degrees (asshown in FIG. 5) up to 90 degrees perpendicular to the original VTOLposition shown in FIG. 1.

The angles in the swiveling joints 23, which also allow the passage ofthe flow to the elements 17, 18, can be gradually changed to allow aperfect balancing of the aircraft from hover to gaining speed andincrease the lift of the wings of the aircraft at forward velocities of,e.g., 10% more than stall velocities of the aircraft. For example, anaircraft according to an embodiment of a VTOL aircraft may reach a speedof 50 mph within a few tens of seconds after hovering at a fixed point,while still balancing some of the weight via FPS 17, 18 pointing at 45degrees upwards in the direction of flight, and still accelerating inthe forward direction while the wings begin supporting, e.g., 50% of theweight of the aircraft flying forward. At this point in time and whilethe aircraft is rapidly still accelerating to 100 mph, FPS elements 17,18 are moving into perfectly horizontal position (90 degrees or moreperpendicular to their original VTOL position) and a balance between thedrag force and thrust is achieved using purely the FPS system (i.e., allair 22 is routed via ports 13 and 14 to supply the FPS elements withmotive fluid). Close to a forward air speed of, for example, 150 mph,the vanes 16 begin to open and allow the air stream 22 to pass throughthe vanes thus pushing the aircraft forward in a faster manner. Duringsaid transition to fully wing-borne operation, the augmentation ratio ofthe FPS is lowered due to the increasing ram drag imposed by theincoming air into the FPS elements 17, 18. The final thrust obtained inwing borne operation can be increased by switching to fully open vanes16 as shown in FIGS. 2 and 4 and closing valves 15 thereby blocking theair supply to the ports 13 and 14 and forcing the entirety of air 22 toexit the plenum 12 via vanes 16 resulting in an accelerated stream 25and propelling the aircraft in the forward direction and wing-borne modeat speeds that can be modulated by the RPM of fan 21.

In this manner, an embodiment solves the problem of mismatches betweenseparate takeoff and cruise powerplants by using the same powerplant tosupply the mechanical work via shaft 11 to the fan 21. In addition,reduction of fuel flow to the main gas turbine providing mechanicalpower results in slowing down the fan 21 similar to a turbofanoperation. By shutting off the air to the FPS elements 17, 18 at the endof the transition and during fully wing-borne high-speed flight, the fanspeed reduction via mechanical work reduction will result in fuelsavings and will allow a much wider flight envelope in altitude, speed,and maneuverability, since the aircraft will require significantly lowerthrust for forward moving. For instance, 30% of the thrust needed forVTOL using the FPS elements 17, 18 can now be supplied by using thenozzle vanes 16 for high speed cruising whilst operating the fan 21 atlower than maximum speed. This means adjusting to a thrust calculatedwith an augmentation ratio of 1.0 per Equation 2:

$\begin{matrix}{{15\mspace{14mu} {{kg}/s}*\sqrt{1.4*287\frac{J}{kgK}*353\mspace{14mu} K}} = {5.65\mspace{14mu} {kN}}} & {{Eq}.\mspace{14mu} 2}\end{matrix}$

when the aircraft is in full wing-borne mode. A typical general aviationaircraft achieving such thrust would have no problem accelerating tospeeds exceeding 400 mph and high altitudes. Conversely, a transitioncan be achieved for transferring from cruise, as illustrated in FIG. 6,to hovering via closure of vanes 16 and forcing the air through ports 13and 14 to open the FPS operation and reverse the swiveling movement ofFPS elements 17, 18 from nearly horizontal and embedded into thefuselage of the aircraft to nearly vertical position for hovering orlanding. With the rotation of FPS elements 17, 18, they can also be usedas air brakes slowing down the aircraft to a point where gradually thewings provide less lift and the elements 17, 18 provide most of thebalance to the weight of the aircraft. At the point where the aircrafthas slowed down sufficiently and is nearly stationary in the hoveringmode, the modulation of the fan 21 (now operating with vane system 16fully closed and ports 13 and 14 fully opened) allows for the thrust todecrease to a point where the aircraft lands.

Such a system has the following advantages:

No moving parts for FPS elements 17, 18 other than swiveling of theelements to help with smooth transition from vertical to cruise (wingborne) operation.

Minimization of complexity.

Low temperature of the air discharge from the fan 21 with modes 1.8pressure ratio means low temperature and lightweight materials can beused for the FPS elements 17, 18, such as thermally resistant plasticcomposites.

Maintenance is much easier to achieve.

High speed can be achieved in cruise by switching to fan type ofoperation.

The gas turbine can be replaced with an electric motor for use withbatteries of high energy density.

A high-efficiency system and same size turboshaft turbine can be usedhence minimizing cost and weight.

An embodiment of an aircraft 40 can be further refined by integratingthe FPS system into aerodynamic control surfaces, such as airfoils, fordecreased drag during high-speed flight. Such an embodiment isillustrated in FIGS. 7 and 8. In FIG. 7, propulsive elements 30, 31,similar in functionality to that of elements 17, 18, are rotated to ahorizontal configuration to match the profile of the main aircraft wing41. In this configuration, thrust is solely generated through theturbofan nozzle 16, and valves 15 are closed preventing airflow throughFPS elements 30 and 31. As illustrated in FIG. 8, the FPS propulsiveelements 30, 31, as well as accompanying surfaces 32-37, are rotatedrelative to wing 41 so that thrust is generated upwards for hover andVTOL. In this configuration, the variable nozzle vanes 16 are closed andall airflow is directed through the FPS elements 30 and 31.

FIG. 7 illustrates the geometry of this alternate embodiment. Compressedair is directed from the main plenum 12 into wall jets (not shown) indevices 30, 31. These wall jets entrain ambient air at a high bypassratio through the slot-shaped periphery across trailing surfaces 32, 33.Surfaces 32 and 33 are partially circumscribed by sidewalls 34 a, 34 b,35 a, 35 b. These sidewalls taper toward the airfoils trailing edges 36and 37.

In FIG. 7, the surfaces 32, 33 play a role in generating more lift (liftaugmentation) at angles shallower than 45 degrees to the horizontal(direction of flight). In this case and at the speeds of interest, thesuction side of the surfaces 32, 33 that see the emerging flow from theelements 30 and 31 will experience a larger local velocity compared tothe aircraft 40 velocity. In this case, and just prior to switching tothe turbofan nozzle jet modus operandum, the additional lift generatedby the difference in pressures on the suction and pressure sides of thesurfaces 32, 33 will create more lift, as it is known in the industryand by the conditions dictated by Bernoulli. The moment of switch fromusing elements 30 and 31 for propulsion during VTOL, acceleration andclimb of the vehicle, to guiding the compressed air through the nozzlevanes 16, is anticipated to coincide with best conditions for which theaircraft is moving at fastest, safe speeds, in good coordination withthe valves 15 making the switch and attitude of the aircraft 40. Theswitch to using the compressed air as a motive/primary air to thethrusters (elements 30 and 31) with entrainment to a direct jet viaexpansion through nozzle vanes 16 at high speeds will coincide with thepoint where elements 30 and 31 incur a too-large RAM drag via entrainedair to possibly produce enough net force to further accelerate theaircraft 40. For example, a vehicle employing this system may accelerateto speeds in the range of 150-200 mph and reach steady-state flight; forthe vehicle to accelerate to 400 mph the switch is required. The vehiclemay hence suffer an increase in velocity as well as in fuel consumption,due to the elements 30 and 31 no longer being employed and producing nolonger a net force sufficient for acceleration. At this point, the airmass entrainment by these elements and hence thrust augmentation mayfall below the acceptable levels, and a switch to use the compressed airflowrate via expansion in nozzle vanes 16 allows for furtheracceleration. At this point the thrusters 30, 31 would be able to bealigned with a streamlined profile reducing the drag and the RAM dragexisting while in operation. The reverse is valid for slowing down andflying economically in lower speed regimes, at lower speeds but higherefficiency. Such a system results in the fastest possible commercial ormilitary application with VTOL capability.

The switch from thrusters (fluidic) entrainment mode to fan mode resultsin an optimized thermal and propulsive efficiency between the tworegimes. In a regime lower than 125 mph approximately, a high thermalefficiency and better propulsive efficiency is obtained using thefluidic (thrust augmentation) via entrainment of ambient air, even ifRAM drag increases with entrainment. The entrainment ratio may be forinstance >10 and the velocity emerging for the mixture of compressed andentrained air may reach 105 m/s (235 mph). As entrainment diminishes andRAM increases with speed, a switch to use the entire primary air asdirect jet is made beyond 125 mph. This way the thermal efficiencyincreases at a different rate and a high overall total efficiency, asthe product between the propulsive and thermal efficiencies is obtained.

One or more embodiments of the invention include the following features:

A VTOL suitable propulsion system that can transfer thrust for anaircraft from vertical flight to wing borne flight consisting of a fanor compressor, a plenum in communication with a set of vanes that canfully open and close and having at least one other opening that canfully open and close to route said fan discharge air from fan to asecondary thrust augmenting system.

A system in which the secondary thrust augmentation system produces anaugmentation between 1.25 and 3.

A system in which the fan produces a pressure ratio between 1.1 and 3.0in said plenum.

A system in which the additional opening port can be opened and closed.

A system in which the secondary thrust system can be swiveled from afully vertical to a fully horizontal position and in addition can beretracted or embedded in a streamlined manner to the fuselage.

A system that has a movable vane system that can turn, accelerate theair to forward cruise speeds, or fully close them to feed anaugmentation system.

An aircraft using the system that can employ a gas turbine as mechanicalwork input to the fan.

An aircraft using the system that can employ an electric motor as driverof the fan.

An aircraft using the system that can employ a hybrid system as driverof the fan.

An aircraft employing multiples of the system in which the secondarythrust system is swiveled to minimize drag and become inactive while thefan air is directed fully through a single propelling nozzle.

Although the foregoing text sets forth a detailed description ofnumerous different embodiments, it should be understood that the scopeof protection is defined by the words of the claims to follow. Thedetailed description is to be construed as exemplary only and does notdescribe every possible embodiment because describing every possibleembodiment would be impractical, if not impossible. Numerous alternativeembodiments could be implemented, using either current technology ortechnology developed after the filing date of this patent, which wouldstill fall within the scope of the claims.

Thus, many modifications and variations may be made in the techniquesand structures described and illustrated herein without departing fromthe spirit and scope of the present claims. Accordingly, it should beunderstood that the methods and apparatus described herein areillustrative only and are not limiting upon the scope of the claims.

What is claimed is:
 1. A propulsion system for an aircraft, comprising:a plenum having an intake port and an output port; a fan coupled to amotor configured to power the fan, the powered fan configured tocompress ambient air entering the intake port; one or more ejectorsfluidically coupled to the plenum via one or more valves; and a nozzledisposed within the output port, the nozzle comprising a set of vanes,wherein: the system operates in a first configuration in which thenozzle vanes are closed and the compressed ambient air exits the plenumonly through the one or more valves into the one or more ejectors, andthe system operates in a second configuration in which the one or morevalves are closed, the nozzle vanes are open and the compressed ambientair exits the plenum only through the output port.
 2. The system ofclaim 1, wherein the ejectors are rotatable through at least a 90° anglewith respect to the plenum.
 3. The system of claim 1, wherein the one ormore ejectors comprise: a convex surface; a diffusing structure coupledto the convex surface; at least one conduit coupled to the convexsurface and configured to introduce to the convex surface a primaryfluid produced by the vehicle; and an intake structure coupled to theconvex surface and configured to introduce to the diffusing structure asecondary fluid accessible to the vehicle, wherein the diffusingstructure comprises a terminal end configured to provide egress from thesystem for the introduced primary fluid and secondary fluid.